Grid Connection Using a Structure That Combines a Buck Converter and a Push-Pull Converter to Reduce the Low-Frequency Current Ripple of the Fuel-Cell

Abstract

In a grid-connected power generation system using a fuel cell, the low-frequency ripple component must be maintained within an allowable range to improve the lifespan and efficiency of the fuel cell. We propose a grid connection method using a structure that can reduce the low-frequency ripple component of the fuel cell output current by combining a buck converter and a push-pull converter. The proposed converter has a structure in which the inductor of the non-isolated dc-to-dc converter and the current source inductor are shared. Although it is a two-stage structure, it has the same number of inductors as the single-stage method, and the capacitor, an intermediate voltage source, can be removed. The high-frequency transformer is designed so that the rated output is possible even at the lowest output value of the fuel cell. The current peak value of the push-pull converter is reduced by operating the buck converter’s switching frequency at twice the push-pull converter’s switching frequency. The operation mode of the proposed converter and the controller design method will be described in detail. A grid-connected inverter is constructed using the proposed converter, and the feasibility of the proposed approach is verified through simulations and experiments on a 1kW prototype.

Keywords

• Converter
• fuel-cell
• grid-connected
• inverters
• push-pull
• total harmonic distortion (THD)